Method and apparatus for delivering sequential shots to multiple cavities to form multilayer articles

ABSTRACT

Method and apparatus for sequentially delivering multiple shots of polymer material to a plurality of mold cavities to form multilayer articles. A first shot of greater than 50% of the total article weight of a first polymer material is simultaneously delivered to a plurality of mold cavities using, at each cavity, a chamber of predetermined volume that is prefilled with the first polymer material. A second shot of no greater than 10% of the total article weight of a second material is simultaneously delivered to all of the cavities beginning subsequent to the step of delivering the start of the first shot delivery step. The second shot of second material is delivered through a manifold channel that fluidly communicates with each cavity, and is injected to all cavities under pressure exerted by a source of the second material that is common to all of the plurality of cavities.

FIELD OF THE INVENTION

The present invention relates to the delivery of sequential shots ofpolymer material to multiple mold cavities to form multilayer articles,and more specifically to forming multilayer preforms having interiorlayer(s) of relatively low weight percentage and substantially uniformheight (across multiple cavities).

BACKGROUND OF THE INVENTION

Sequential injection molding processes for performing sequential shotsof different polymer materials are well known. To accomplish suchprocesses, various apparati have been developed using hotrunner systemsthat are designed to deliver sequential shots of polymer material to aplurality of cavities. In multicavity applications, shots are intendedto be delivered at the same time in the same amounts and at the samerates of flow by controlling the length and configuration of thehotrunner flow channels and the temperature of various portions of thehotrunner and injection nozzles to each cavity. However, in practice, itis very difficult to achieve such uniform delivery to multiple cavities.

When a single source of polymer material is used to effect flow throughall channel paths in a hotrunner to multiple mold cavities, the pressurewill vary between the flow paths even at points within differentchannels that are located the same distance (path length) from thesource of injection. Still further, changes in the polymer material(s)over time, e.g., different batches, sources, temperatures and moisturecontent, can alter the flow characteristics of the material and renderthe system unbalanced.

These types of multi-cavity injection molding systems are in widespreaduse in the food and beverage industry to make multilayer preforms, whichare subsequently blow molded into multilayer containers. In particular,these multilayer preform and container structures enable cost effectiveuse of what are generally more expensive barrier and/or high thermalperformance materials, as one or more layers of the preform. Ideally,the amounts of the expensive barrier or high performance polymermaterials are utilized in relatively thin layers, thus reducing theoverall cost of the preform/container, while a less expensive structuralpolymer comprises the predominant weight percentage of the article.

For example, Continental PET Technologies (CPT) developed a sequentialmultilayer injection process for making three-layer or five-layerpreforms. A typical five-layer preform includes inner and outer exteriorlayers of virgin PET, a central core layer of virgin or recycled (e.g.,post consumer and/or plant scrap) PET, and two thin intermediate barrierlayers between each of the core and exterior layers. A relatively smallamount of barrier material, typically 2 to 5 percent of the totalpreform weight, forms the thin intermediate layers and yet provideseffective barrier (e.g., gas, moisture, flavor) performance. In order toprovide a uniform and consistent barrier layer structure, the CPTprocess utilizes devices, commonly referred to as mold shooting (ormetering) pots, which comprise a chamber of predefined volume that isfilled/prefilled with the polymer material and located adjacent to anassociated cavity. This enables injection of a precise amount of virginPET (greater than 50% of the total preform weight) from a first shootingpot during a first shot injection, followed by a precise amount ofbarrier material (2-5% of the total preform weight) from a secondshooting pot during a second shot injection. A third shot of virgin orpost-consumer PET is injected from a machine shooting pot (the first,second and third shots comprising approximately 95% of the total preformweight). A fourth and final shot of virgin PET is then injected from amachine shooting pot to pack the preform, and clean out thepost-consumer PET from the nozzle in preparation for the next cycle. TheCPT process and multilayer articles are described in one or more of U.S.Pat. Nos. 4,550,043; 4,609,516; 4,710,118; 4,781,954; 4,950,143;4,990,301; 4,923,723; and 5,098,274, the disclosures of all of which areincorporated herein by reference as if fully set forth herein.

The use of mold shooting pots is an effective way to provide preciseamounts of polymer material for the various layers and insure consistentpreform layer structure. However, there is a cost associated withutilizing shooting pots in multicavity systems, namely the associatedcost of providing a shooting pot for each material for each mold cavityand the expense in providing sufficient physical space in the machineplaten to accommodate all of these shooting pots. As a result of theincreased demand for platen space, the preform manufacturer is generallyrequired to purchase a larger more expensive, higher tonnage machine,even though the increased tonnage is not required. Also, when multipleshots of polymer material are affected using metering pots, the sequenceand timing of the shots becomes cumbersome and more time-consuming inhaving to complete all shots of all polymer materials from multiplemetering pots mounted in multiple locations on a hotrunner/manifold.

For these reasons, others have attempted to rely on balanced manifoldsfor delivering each of the multiple layer materials. However, whileavoiding the cost and space constraints of shooting pots, these systemsdo not consistently produce uniform layer structures in the preform.

It would thus be desirable to provide alternative injection moldingsystems for forming multilayer articles in multiple cavities,particularly in the manufacture of multilayer preforms utilizingrelatively low weight percentages of select (e.g., barrier layer)materials but requiring formation of a consistent layer structure acrossmultiple cavities.

SUMMARY OF THE INVENTION

In accordance with the present invention, a new method and apparatus areprovided for delivering sequential shots of polymer materials tomultiple mold cavities to form multilayer articles. It has been foundthat selective use of shooting pots can produce multilayer structureswith substantially different weight percentages of layer materials but arelatively uniform layer structure, across multiple cavities.

In one embodiment, a method and apparatus are provided for forming afive-layer preform having two relatively thin intermediate interiorlayers, comprising no greater than 10% of the total article weight,which method/apparatus does not require the use of shooting pots fordelivering this low weight percentage interior layer material. Aseparate mold shooting pot (for each cavity) is used to deliver a muchgreater amount, greater than 50% of the total article weight, of a firstshot which forms the exterior inner and outer layers of the article. Incontrast, the low weight percentage second shot can be delivered to allcavities from a common source. The remaining relatively large volume(s)of polymer material(s) can be delivered from one or more sources.

Thus, contrary to what was previously deemed a required use of shootingpots to deliver consistent amounts of a relatively low weight percentageof barrier material for the thin intermediate layers (i.e., in order toinsure that the barrier material layer(s) extended along a predeterminedlength of the preform and/or were of a predetermined thickness toprovide the required barrier performance), it has now been found thatone can rely upon delivery of the barrier material from a common sourceof injection material (common to multiple mold cavities). While therewill be variations in the amount of barrier material delivered, thefaster injection (lower injection time due to lower volume of material)of the second shot, and the controlled amount of the relatively largevolume first shot, produces a substantially uniform height of the secondshot interior layer(s). This finding is counterintuitive to priorexpectations that even a minor variation in the amount of a relativelysmall shot, would produce a greater variation in layer structure(because the variation comprises a larger percentage of a smallervolume).

In accordance with one embodiment, there is provided a method ofsequentially delivering multiple shots of polymer material to aplurality of mold cavities to form multilayer articles, the methodcomprising:

delivering a first shot, for forming an exterior article layer of apredetermined volume of greater than 50% of the total article weight ofa first polymer material, simultaneously to a plurality of mold cavitiesusing, at each cavity, a chamber that is pre-filled with the firstpolymer material to deliver the predetermined volume of the firstmaterial separately to each mold cavity;

delivering a second shot comprising up to 10% of the total articleweight of a second material, simultaneously to all of the cavitiesbeginning subsequent to the start of the first shot delivery step; and

delivering one or more additional shots of material to form themultilayer article;

wherein the second shot delivery step comprises injecting the secondshot of the second material through a manifold channel that fluidlycommunicates with each cavity, the second shot being injected to allcavities under pressure exerted by a source of the second material thatis common to all of the plurality of cavities.

A third shot may be delivered through a manifold channel that fluidlycommunicates with each cavity, the third shot being injected underpressure exerted by a source of a third material that is common to allof the plurality of cavities.

The second shot delivery step may begin upon completion of delivery ofthe first shot to all of the plurality of cavities. Similarly, the thirdshot may begin following completion of delivery of the second shot toall cavities.

In various embodiments, the weight of the second shot of material is: nomore than about 10%, no more than about 8%, or no more than about 5%, ofthe total article weight.

The first shot delivery step may deliver a structural polymer materialas the first polymer material, while the second shot delivers a barrier(or other high performance) polymer material as the second polymermaterial. The third shot may comprise a structural and/or recycledmaterial as the third polymer material.

In accordance with one method embodiment, the second shot delivery stepbegins prior to completion of the first shot delivery. Furthermore, athird shot delivery step may begin with or after start of the seconddelivery step and prior to completion of the first delivery step. Thesecond shot may deliver a barrier polymer material, and the first andthird shots deliver the same or different structural polymer materials.

In accordance with another embodiment of the invention, an injectionmolding apparatus is provided comprising:

a plurality of mold cavities, each cavity fluidly communicating withfirst, second and third fluid delivery channels that respectivelydeliver first, second and third shots of first, second and third polymermaterials sequentially to each mold cavity;

the first fluid delivery channel having separate channel portionsindividually fluidly communicating with a separate corresponding cavity,each channel portion having a separate fluid injection chamber thatseparately communicates with a corresponding cavity and separatelycontains and delivers a predetermined volume of greater than 50% of thetotal article weight of the first material during the first shot to acorresponding cavity;

the second fluid delivery channel fluidly communicating with a commonsource of injection of the second material, the common source ofinjection exerting a pressure that simultaneously delivers a volume ofup to 10% of the total article weight as the second shot of secondmaterial to all of the plurality cavities beginning subsequent to thestart of the delivery of the first shot to each cavity.

The common source of injection of the second material may comprise aninjection screw or a fluid chamber that commonly communicates with anddelivers the second material simultaneously to each cavity.

At least one or the other of the second channel and each cavity mayinclude a heating mechanism for independent control of the temperatureof the second material flowing into or through each cavity.

Each cavity may fluidly communicate with a separate correspondingnozzle, each nozzle having first and second bores respectivelycommunicating with the first and second channels for delivering thefirst and second shots respectively and sequentially to a correspondingcavity.

Each of the separate fluid injection chambers may include a first drivemechanism, the common source of injection of the second material mayinclude a second drive mechanism, and the apparatus may include acontroller that times and directs the operation of the first and seconddrive mechanisms to effect initiation of delivery of the second shotupon completion of delivery of the first shot to all cavities.

The method and apparatus of the present invention are useful in themanufacture of multilayer plastic articles, such as preforms for makingbottles and other food packaging containers. The polymer materialstypically include a structural material and a barrier (e.g., to inhibitthe passage of gas, moisture, flavor, etc.) or other higher performance(e.g., higher thermal resistance for hot-fillable, refillable orpastuerizable containers) material, or a lower cost material (e.g.,recycled post-consumer articles and/or plant scrap). For example, astructural and/or thermal resistant material may be injected as thefirst shot, and the barrier and/or recycled material injected as thesecond shot. As a third shot, a structural, barrier and/or recycledmaterial may be used.

Other combinations of polymer materials in the various layers arepossible and included in the present invention. For example, arelatively less expensive polymer may be used as the larger volumelayers, combined with a relatively more expensive polymer as the smallervolume layers (second shot). Any one or more layers may provide enhancedstructural or other functional properties (e.g., thermal resistance,delamination resistance, etc.). Also, as used herein, first, second andthird polymers is not limited to different polymers, and polymers isused broadly to include copolymers, mixtures, blends, etc.

These and other features of various embodiments of the invention may bebetter understood by referring to the following description inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a multi-cavity mold system where each moldcavity fluidly communicates via a hotrunner channel system with a commonsource of pressurized fluid material, each mold cavity filling at adifferent rate during a single injection cycle;

FIG. 2A is a schematic side, cross-sectional view of a five-layerpreform and FIG. 2B is an enlarged fragmentary sectional view of aportion of the multilayer wall of the preform;

FIG. 3A is a schematic side, cross-sectional view of a blown bottle madefrom the five-layer preform of FIG. 2A, and FIG. 3B is an enlargedfragmentary sectional view showing more specifically the multilayer wallof the bottle;

FIGS. 4A-4D are schematic side, cross-sectional views of a single moldcavity showing the progress of travel of polymer material flow into thecavity as a result of first, second, and third shots of polymermaterials that are sequentially injected to form a five-layer article;

FIG. 5 is a schematic view of a multi-cavity injection molding system,according to one embodiment of the present invention (showing only asingle cavity for ease of discussion), where three different materialsare controllably injected into each cavity;

FIG. 6 is a schematic view of a multi-cavity injection molding systemwhere the timing of the delivery of material to each cavity iscontrolled via a controller;

FIGS. 7A-7D are schematic side, cross-sectional views of amulti-position actuator/valve pin and associated multi-bore nozzleusable in select embodiments of the invention;

FIGS. 8A-8D are schematic side, cross-sectional views of a single moldcavity showing the progress of travel of polymer material flow into thecavity as a result of first, second, and third shots of polymermaterials that are injected to form a three layer article, in accordancewith another embodiment of the invention; and

FIG. 9 is a schematic side, cross-sectional view of an actuator/valvepin and associated multi-bore nozzle usable in the embodiment of theFIG. 8.

DETAILED DESCRIPTION

FIG. 1 shows schematically an injection molding system having amultiplicity of essentially identically shaped cavities 14 a-14 i thatare fed by a single source of polymer material 10. The system shown inFIG. 1 does not include shooting or metering pots to assist incontrolling the amount or pressure of material flow to each cavity, butrather uses only the single source 10 of injection that provides all ofthe pressure by which the injected polymer material is forced to flowthrough all of the various and different manifold channels 12 a-12 c andinto all of the multiple number of cavities 14 a-14 i. As shown, theforward most progress of travel of polymer material into each cavity 14a-14 i is different for each cavity, the top or leading edge level ofpolymer material within each cavity varying in distance either above orbelow travel line 16 as shown in FIG. 1. These differences in rate andvolume of material filling of identically shaped cavities typicallyarise out of minor differences in the size, shape, length andtemperature of the path of channel travel from the source 10 through thechannels 12 a-12 c to the separate cavities, as well as minordifferences in the cavities 14 a-14 i themselves. Such differences inflow rate can be caused by very small differences between channel pathsor cavities (e.g. tenths of millimeters in length or diameter orfractions of a degree in temperature) but such differences still resultin the differences in fill rate among different cavities as shown inFIG. 1. Even small differences in fill rate can have a significanteffect on the structure of the molded articles, e.g. the location of aninterior barrier layer in a multilayer preform.

It has been found that injecting a relatively large amount of the firstlayer material in a precisely desired (i.e., metered) amount to each oneof a multitude of mold cavities is important to achieving a properlayering within the cavities of a second relatively small amount of asecond injected material. Methods and apparati for carrying outsequential first, second and third shots of materials arise in a varietyof contexts pertinent to the present invention and are described by wayof the following examples.

A typical embodiment of a three-material (3M), five-layer (5L) moldedarticle is illustrated in FIGS. 2A-2B (preform) and FIGS. 3A-3B(bottle). A multilayer preform 110 manufactured by an injection moldingprocess is shown in FIG. 2A. The multilayer preform 110 has a centralinterior core layer 130, two intermediate interior layers 136 and 138 onopposite sides of the core layer, and exterior inner 132 and outer 134layers. The bottle 210 shown in FIG. 3A is made from the preform 110 bya blow molding process. Similar to the preform, the wall of the bottlehas a central interior core layer 230, two intermediate interior layers236, 238 and exterior inner and outer layers 232, 234. In a typicalembodiment of a multilayer preform and/or bottle, the core 230 andexterior layers, 232, 234 of the bottle (FIG. 3B) and/or the core 130and exterior layers 132, 134 of the preform (FIG. 2B), are comprised ofa structural polymer; the structural polymer of the core layer maydiffer from that of the exterior layers. The relatively thin (lowvolume) intermediate layers of the bottle (236 and 238) and the preform(136 and 138), are typically comprised of another more expensivepolymer, such as a barrier or other high performance polymer. Typicalexamples of multilayered preforms, bottles and packages and the specificcompositions of the various layers of such multilayer objects aredisclosed in U.S. Pat. Nos. 4,781,954; 4,863,046; 5,599,496 and6,090,460, the disclosures of all of the foregoing of which areincorporated herein by reference in their entirety.

FIGS. 4A-4D illustrate a three-shot multilayer injection molding processfor forming the five-layer, three-material preform of FIGS. 2A-2B. Thepreform is formed in a mold cavity 466 between an outer mold 303 andinner core 302 of a conventional injection mold. A first shot of firstpolymer material 318 is injected into a proximal end (gate) of a moldcavity 466 and as it flows through the mold cavity, due to therelatively cool temperatures of the outer mold 303 and inner core 302,there will be solidification of the first polymer material on both theinner and outer walls of the mold cavity/core to define exterior inner304 and outer 306 preform layers (layers 132 and 134 in FIG. 2B) of thefirst material. In FIG. 4A, the relatively large volume of first shotmaterial has progressed part way (roughly half way) up the mold cavitywalls. In FIG. 4B, a second shot of a second polymer material 320, e.g.,a barrier material, is injected into the bottom of the mold cavity. Therelatively small amount of barrier material 320 may pool at the lowerend of the cavity. A relatively large third shot 322 of a third polymermaterial is then injected into the gate at a pressure which causes thesecond shot material 320 to be pushed up the mold cavity to form innerand outer intermediate preform layers 309, 310 (layers 136 and 138 inFIG. 2B), while the third material 322 forms a central core preformlayer 328 (layer 130 in FIG. 2B). The tunnel flow of the second 320 andthird 322 shots, between the exterior layers 304 and 306, enables theformation of relatively uniform and thin interior intermediate layers309 and 310 of the barrier material 320, and a thicker core layer ofmaterial 322. Finally, the advancing layers reach the distal end of themold cavity, producing the five-layer preform structure having interiorintermediate and core layers extending up into the neck finish (as shownin FIG. 4D). Alternatively, the interior layers 309, 310 and 328 mayextend only partially up the preform wall and terminate, for example,below the preform neck finish 114 (FIG. 1). Still further, a fourth shot(of for example the first material 318) may be injected after the thirdshot in order to clean the nozzle of the third shot material 322 and/orform a further interior layer in some or all of the preform base (notshown), thus fully sealing the second and third shot materials fromoutside exposure. As used herein, the intermediate 309, 310 and core 328layers are considered “interior” layers whether or not a minor portionat the base is exposed. The above-described process is given by way ofexample only, and is not meant to be limiting; many other processes maybe used to form multilayer articles, including articles other thanpreforms.

FIG. 5 shows one embodiment of an injection molding system 4 accordingto the invention. This embodiment is capable of carrying out a 3-shot,5-layer process as described with reference to FIGS. 4A-4D. The system 4includes an inner core 302 and outer mold 303 cavity set, an associatednozzle 468 and actuator 400, a manifold 18, and three separate sources20, 22, 34 of first, second and third polymer materials. For purposes ofdiscussion, only one mold cavity 466 is shown in FIG. 5.

A first source (e.g, screw/barrel) 20 supplies the first shot materialthrough a common feed manifold channel 44. Each separate cavity isseparately provided with a metering (a/k/a shooting) pot 36 to ensurethat a precisely metered amount of the first shot of structural materialis injected into the associated cavity via a separate channel portion 48that specifically communicates with an individual cavity 466. In FIG. 5,metering pot 36 feeds channel portion 48 that feeds cavity 466, it beingunderstood that a separate metering pot and associated separate channelportion is separately provided for each one of the multiplicity ofcavities (not shown in FIG. 5) in a multi-cavity system. The commonchannel feed portion 44 communicates with all of the cavities and witheach individual channel portion 48 via valve 38. Valve 38 is closed atthe start of the first shot in order to separate and close channelportion 48 and metering pot 36 off from communication with the rest ofthe system, such that metering pot 36 can separately control the fluidmaterial pressure in the cavity 466 and its associated nozzle channel.In the present embodiment, the nozzle 468 has a central axial bore 460and two side bores 458 and 462 (shown in greater detail in FIGS. 7A-7C).An actuator assembly 400 moves a valve pin 450 within central bore 460to control the opening and closing of all of the nozzle bores 458, 460,462 according to a predetermined program. The nozzle actuator 400 (shownonly schematically in FIG. 5) can be a single piston/chamber actuator(as shown in the specific embodiment of FIGS. 7A-7C), a multiplepiston/chamber, or any other known actuator design suitable for use ininjection molding valve pin applications. A controller, described belowwith reference to FIG. 6, is provided to control valves 38, 39, 40, 50,62, 63 to control flow through selected bores of the nozzle 468.

Unlike the first shot, the second shot material, e.g. a gas barrier(passive or active) material, is commonly fed to the multiplicity ofcavities from a common single second source (e.g., screw/barrel) 34 viaa common manifold channel 42. As described with reference to the firstshot, each separate cavity is provided with a separate channel portion46 that feeds cavity 466. As shown, the common channel feed portion 42communicates with individual channel portion 46 by valve 40 which istypically closed during the course of the first shot and up until thestart of the second shot. Valve 40 separates and closes channel portion46 off from communication with the rest of the system. Feed channel 46communicates with an axially offset feed bore 462, within the body ofnozzle 468, to feed the gate 464 (see FIGS. 7A-7C). When valve 40 isopened at the conclusion of the first shot, either screw/barrel 34, or amachine (master) shooting pot that is common to all cavities (notshown), provides all of the pressure necessary for delivery of thesecond shot of material to all of the cavities in the multicavitysystem. The second shot of material can be delivered in such arelatively imprecise manner (e.g., ±20% of the desired weight of thesecond shot layer in the article) because the first shot of material(see FIG. 4B) has been previously delivered in a precisely meteredvolume. In certain applications, a greater amount of the second shotbarrier material may be provided so that all cavities receive at least aminimum volume of the barrier material (e.g., to insure a predeterminedminimum barrier height is met in each cavity/preform). In manyapplications, the second shot of the second material is preferably notcommenced to any one of the multiplicity of cavities until the firstshot of the first material has been completely delivered to all of thecavities. However in other applications, the second shot may be startedafter the first shot begins but before it is finished, so that there issome amount of simultaneous delivery of the first and second (and third)shots. As used herein, sequential means one shot starts after a priorshot, but some overlap in the delivery is not precluded.

The metering pots 36 for feeding the first shot to the individualcavities are typically arranged and adapted to be mounted on thehotrunner or manifold 18 portion of the system 4 such that theindividual metering pots can be readily interconnected for fluidcommunication with each individual manifold channel portion 48 thatseparately communicates with an individual cavity. By contrast, a mastermetering pot (such as metering pot 56 for the third shot as describedbelow), can be mounted and provided on the injection mold machine itself(as opposed to the manifold 18) for purposes of acting as a commonsource of stored and ready material for simultaneous and common feed toall of the multiplicity of cavities.

In the embodiment shown in FIG. 5, a machine metering pot 56 is fluidlyconnected to the third source (screw/barrel) 22 for injecting a thirdshot material (see FIGS. 4C-4D). The third shot is delivered to the samegate 464 through a third bore 458 in nozzle 468 that terminates at andcommunicates with the same gate 464 as nozzles bores 460, 462. Prior tothe start of the third shot, the machine metering pot 56 is filled andthe valve 62 closed. The valve 63 is opened at the start of the thirdshot to all cavities. The common manifold channel portion 58communicates with and allows simultaneous injection of the third shot toall of the multiplicity of cavities. One of the primary purposes of theuse of the machine metering pot 56 is to ensure that an excess of fluidmaterial is always present in the system between the screw/barrel 22 andthe cavities 466 to be ready for injection from one injection cycle tothe next. The machine metering pot 56 is a common source of materialfeed and provides all of the pressure necessary to deliver the thirdshot of the third material to all of the multiplicity of cavities. Asdescribed above, a similar machine metering pot could be employed inconnection with carrying out the second shot.

As shown schematically in FIG. 6, delivery of material to each separatecavity of a multi-cavity system can be mechanically controlled withvalve pins 27 a-d that are reciprocally movable via fluid drivenactuators 26 a-d. The actuators are driven by fluid that is controllablyinput and output to the actuators' cylinders via fluid pumps 20, 22and/or valves 24 a-d. Timed control over the drive of the pumps 20, 22and/or the opening/closing of valves 24 a-d can be carried out by use ofa controller 28 according to a predetermined program loaded in theprocessor and/or memory of controller 28. Controller 28 typicallycomprises a microprocessor or other digital data processing/storageapparatus.

FIGS. 7A-7C show one embodiment of a nozzle design and process fordelivering selected amounts of three materials in three successive shotsto a cavity at predetermined times during the course of a singleinjection cycle. As shown, the actuator system 400 comprises an actuatorhaving a single piston 412 sealably mounted within a chamber 414 forreciprocal fluid-driven (hydraulic or pneumatic) movement of the piston412 and any associated/attached parts, such as valve pin 450, along axisX. In the manner described with reference to FIG. 6, controller 28directs the drive of the actuator piston 412 according to a program thatprecisely times the operation and movement of the valve pin 450 betweenthe multiple positions shown in FIGS. 7A-7C in synchronization with theoperation of the drive mechanisms for the metering pot 36, the screws20, 22, 34, the valves 38, 39, 40, 50, 62, 63 and any associatedoperational components of the system. In multi-cavity applications, thecontroller 28 is typically interconnected to and simultaneously directsthe drive of all of the multiplicity of actuators, valves, screws,metering pots and the like during a single injection cycle.

In one embodiment, FIG. 7A shows a start position of the actuator 400and the valve pin 450 in a typical three material shot injection cycle.In FIG. 7A, all three material flow channels 458, 460 and 462 are closedat the beginning of a cycle such that there is no flow of any of thethree materials into or through the gate passage 464 to the cavity 466.

As described with reference to FIG. 5, the first shot of virgin materialis delivered from the metering pot 36 through a central axial bore 460in the nozzle 468. At the start of the first shot, the controller 28instructs the actuator 400 to retract the valve pin 450 to the positionshown in FIG. 7B where the tip end of the central bore 460 is opened andmaterial flow through central bore 460 into gate 464 of cavity 466 isenabled. Once the first shot is underway, cavity 466 begins to fill inthe manner and profile shown schematically in FIG. 4A.

To begin the second shot, the controller instructs the actuator 400 tomove the pin 450 to the position shown in FIG. 7C to close the centralaxial bore 460 (feeding the first shot material) and enable flow of thesecond material through nozzle bore 462. Simultaneously the controller28 instructs either valve 40 to open or screw 34 to operate (or both) inorder to coordinate the start of the flow of the second material withthe opening of nozzle bore 462. Once the injection flow of the secondshot is underway, the second material flows through each individualmanifold channel portion 46, each second nozzle bore 462 and eachindividual gate 464 into each individual cavity 466 to achieve thesecond shot fill profile shown in FIG. 4B. As described herein, the useof an individual metering pot for use in delivering the second shot iseliminated.

In the embodiment illustrated in FIG. 5 where a third shot of a thirdmaterial is delivered simultaneously to all cavities via a commonmanifold channel 58, the third shot is preferably commenced uponcompletion of the second shot to all cavities. The third shot iscommenced (either simultaneously to all cavities or at separate times)by moving the valve pin 450 and associated actuator 400 back to aposition as shown in FIG. 7D, where at least the tip end of the thirdmaterial bore 458 is open to communication with gate 464 and cavity 466,allowing the third shot polymer material to push up in the second shotmaterial in the mold and form a five layer preform. Controller 28simultaneously directs the movement of the pin 450, actuator 400, valves62, 63 and metering pot 56 to precisely begin and end the flow of thethird shot. At the conclusion of the third shot, the valve pin 450 isdirected to move back to the FIG. 7A closed position.

FIGS. 8-9 illustrate another embodiment of a method and apparatusaccording to the invention for making a three layer preform. FIGS. 8A-8Bshow a sequence of steps of filling a mold with multiple polymermaterials to form the three layer article, and FIG. 9 shows anassociated valve apparatus for supplying the multiple polymer materialsto the mold cavity.

FIG. 8A shows a first shot of a structural polymer material 518, such asPET, being injected into the gate end of the mold between a core 502 andouter cavity 503. At this point in time, about 80-95% of the total firstshot volume has been injected into the mold cavity; the total first shotweight of PET is approximately 75-85% of the total preform weight. FIG.9 shows a suitable nozzle 568, a valve pin 550 and an actuator assembly500 including piston 512, chamber 514, and controller 528. The nozzle568 has a bore 562 through which the first shot of PET material isintroduced through gate 564 into the mold cavity 556.

FIG. 8B shows a next point in the sequence in which first, second andthird shots 518, 520, 522 respectively are being simultaneously injectedthrough gate 564 into cavity 566. The second shot of barrier polymermaterial 520 is commenced while the first shot 518 continues to enterand fill the mold. In addition, a third shot 522 of structural polymermaterial, here the same PET as the first shot material, is begun withthe start of the second shot barrier material. As shown in FIG. 9, thesecond shot barrier material is supplied by bore 558 and the third shotPET material is supplied by bore nozzle 560, at the same time that bore562 supplies the first shot PET material. In this embodiment, therelative positioning of the first, second and third shot bores differsfrom that in the previous embodiment, and thus the feed sources of FIG.5 would be accordingly modified in a known manner (e.g., an individualshooting pot for feeding the first shot bore 562, a common source forfeeding the second shot bore 558, and another source for feeding thethird shot bore 560).

FIG. 8C shows a next point in the sequence in which the second barriershot 520 has ended, but the first 518 and third 522 shots continue. Asshown, the first shot 518 is almost completely in (approaching the neckfinish 504 end of the preform) and the third shot 522 is still filling(along with completion of the first shot).

FIG. 8D shows a next point in the sequence in which the first and secondshots have now ended, and the third shot 522 continues to be supplied tothe gate for a pack and hold stage as the preform cools and shrinks. Theresulting three layer structure, which extends from within the preformfinish 504 (just above the flange 507) down to the top of the preformend cap 509, includes a central core layer 520 of the barrier materialdisposed between inner and outer exterior layers of PET (formed by thefirst and third shots 518 and 522). The positioning of the layers, theweight percentage of materials, and/or the composition of the materialsmay all be varied in accordance with the desired application.

There has thus been shown various method and apparatus embodiments ofthe invention for producing multilayer articles such as preforms. Theseand other implementations and modifications thereof will be readilyapparent to the skilled person and is included within the scope of theinvention as described in the following claims.

1. A method of sequentially delivering multiple shots of polymermaterial to a plurality of mold cavities to form injection-moldedmultilayer articles, the method comprising: delivering a first shot,forming an exterior article layer of a predetermined volume of greaterthan 50% of the total article weight of a first polymer material,simultaneously to a plurality of mold cavities using, at each cavity, achamber that is pre-filled with the first polymer material to deliverthe predetermined volume of the first material separately to each moldcavity; delivering a second shot, forming an interior article layercomprising up to 10% of the total article weight of a second material,simultaneously to all of the cavities beginning subsequent to the startof the first shot delivery step; and delivering one or more additionalshots of material to form the multilayer article; wherein the secondshot delivery step comprises injecting the second shot of the secondmaterial through a manifold channel that fluidly communicates with eachcavity, the second shot being injected to all cavities under pressureexerted by a source of the second material that is common to all of theplurality of cavities.
 2. The method of claim 1, wherein the step ofdelivering one or more additional shots comprises delivering a thirdshot of a third material through a manifold channel that fluidlycommunicates with each cavity, the third shot being injected underpressure exerted by a source of the third material that is common to allof the plurality of cavities.
 3. The method of claim 1, wherein thesecond shot delivery step begins upon completion of delivery of thefirst shot to all of the plurality of cavities.
 4. The method of claim3, wherein the method includes a step of delivering a third shot ofpolymer material simultaneously to all of the plurality of cavitiessubsequent to the step of delivering the second material to each cavity.5. The method of claim 4, wherein the first shot delivery step deliversa structural polymer material as the first polymer material.
 6. Themethod of claim 5, wherein the second shot delivery step delivers abarrier polymer material as the second polymer material.
 7. The methodof claim 6, wherein the third shot delivery step delivers at least oneof a structural and recycled material as the third polymer material. 8.The method of claim 1, wherein the second shot delivers up to 8% of thetotal article weight.
 9. The method of claim 1, wherein the second shotdelivers up to 5% of the total article weight.
 10. The method of claim1, wherein the article is a preform.
 11. The method of claim 10, whereinthe second shot forms a core layer in the preform.
 12. The method ofclaim 11, wherein a third shot seals the core layer in the preform. 13.The method of claim 10, wherein the second shot forms two intermediatelayers in the preform.
 14. The method of claim 13, wherein a third shotforms a central core layer in the preform.
 15. The method of claim 14,wherein a fourth shot seals the core and intermediate layers in thepreform.
 16. The method of claim 1, wherein the weight of the secondshot is selected to achieve a predetermined minimum height of the secondshot interior layer in the articles formed in all cavities.
 17. Themethod of claim 16, wherein the article is a preform and the minimumheight extends into a neck portion of the preform.
 18. The method ofclaim 1, wherein the second shot delivery step begins prior tocompletion of the first shot delivery step.
 19. The method of claim 18,wherein a third shot delivery step begins with or after start of thesecond shot delivery step and prior to completion of the first deliverystep.
 20. The method of claim 19, wherein the second shot delivery stepdelivers a barrier polymer material.
 21. The method of claim 20, whereinthe first shot delivery step delivers a structural polymer material. 22.The method of claim 21, wherein the first and third shot delivery stepsdeliver the same structural polymer material.
 23. An injection moldingapparatus for sequential delivery of multiple shots of polymer materialto a plurality of mold cavities to form multilayer articles, theapparatus comprising: a plurality of mold cavities, each cavity fluidlycommunicating with first, second and third fluid delivery channels thatrespectively deliver first, second and third shots of first, second andthird polymer materials sequentially to each mold cavity; the firstfluid delivery channel having separate channel portions individuallyfluidly communicating with a separate corresponding cavity, each channelportion having a separate fluid injection chamber that separatelycommunicates with a corresponding cavity and separately contains anddelivers a predetermined volume of greater than 50% of the total articleweight of the first material during the first shot to a correspondingcavity; the second fluid delivery channel fluidly communicating with acommon source of injection of the second material, the common source ofinjection exerting a pressure that simultaneously delivers a volume ofup to 10% of the total article weight as the second shot to all of theplurality cavities beginning subsequent to the start of a delivery ofthe first shot to each cavity.
 24. The apparatus of claim 23, whereinthe common source of injection of the second material comprises aninjection screw or a fluid chamber that commonly communicates with anddelivers the second material simultaneously to each cavity.
 25. Theapparatus of claim 23, wherein at least one or the other of the secondchannel and each cavity includes a heating mechanism for independentcontrol of the temperature of the second material flowing into orthrough each cavity.
 26. The apparatus of claim 23, wherein each cavityfluidly communicates with a separate corresponding nozzle, each nozzlehaving first and second bores respectively communicating with the firstand second channels for delivering the first and second shotsrespectively and sequentially to a corresponding cavity.
 27. Theapparatus of claim 23, wherein each of the separate fluid injectionchambers include a first drive mechanism, the common source of injectionof the second material includes a second drive mechanism, and theapparatus includes a controller that directs the operation of the firstand second drive mechanisms to effect initiation of delivery of thesecond shot upon completion of delivery of the first shot to allcavities.